I read that monster spawns occur in some areas of Lockdown, and hearing that gave me a sort of idea.
Basically a RTS-inspired game that involves summoning monsters. You start off with a base and you can use it to create Mech Knights and other monsters (you get a limit on how much you can do this, of course, as well as what kinds of monsters you summon) and a really huge terrain. In this terrain are neutral monsters and the base of the opposing player
You then lead them around to attack another player or his base or summons (which levels them up).
All the monsters are either versions of clockworks monsters or whole new critters recolored to your team color and either have no elemental typing or bear emblems that depict their element, and without exception will all start at Tier 1 and have to work their way up to Tier 3 by beating up things.
the players have their weapons, armor and shield swapped out for some special (albeit weak) standardized replacements and he gains a bunch of skills relating to controlling his mobs and aiding them in general (basically the player gets to become some kind of equivalent to a hybrid of a Pit Boss, Silkwing, Alpha Wolver, and a Mender but without the OP that would come from actually combining them or the broken elements), but keep their costume armor.
of course this could very well end up being too big and thus necessitating it's own spin-off game :S
Sounds like DOTA :D
I'd be happy with a tower defense kinda game though...
...though like your suggested mode it might take forever to make.